Portable attachment of fiber optic sensing loop

ABSTRACT

The subject matter of this specification can be embodied in, among other things, a system for removably attaching an optical fiber sensor loop onto a tubular member, which includes an optical fiber sensor loop having a continuous optical fiber positioned arranged in a plurality of loops, each of said loops having a first end turn and a second end turn, a first and a second turn guide each including a plurality of turn grooves increasing outwardly in increasing radii, each of said turn grooves configured to receive an end turn portion of the optical fiber, a first and a second supporting wedge each having a planar first surface configured to receive a turn guide and a curved second surface configured to be received on the tubular member, and a connector configured to couple the first mounting wedge to the second mounting wedge.

CLAIM OF PRIORITY

This application is a U.S. National Stage of International ApplicationNo. PCT/US2014/017983, filed Feb. 24, 2014.

TECHNICAL FIELD

This present disclosure relates to an apparatus for mounting of fiberoptic sensing elements on pipe sections.

BACKGROUND

In connection with the recovery of hydrocarbons from the earth,wellbores are generally drilled using a variety of different methods andequipment. According to one common method, a drill bit is rotatedagainst the subsurface formation to form the wellbore. The drill bit isrotated in the wellbore through the rotation of a drill string attachedto the drill bit and/or by the rotary force imparted to the drill bit bya subsurface drilling motor powered by the flow of drilling fluid downthe drill string and through downhole motor.

The flow of drilling fluid through the drill string can exhibitvariations in pressure including pressure pulses. These pressurevariations can cause dimensional changes in solid structures such aspiping that carries the drilling fluid to and from the drill string.Strain gauges are sometimes used for detecting and measuring absolutedimensional changes of solid structures, such a piping for drillingfluid. Such changes can occur gradually, however, and may be challengingto observe and quantify.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an example optical sensor mountingsystem.

FIG. 2 is a perspective view of an example optical sensor loop.

FIG. 3 is perspective view of an inner surface of an example opticalsensor loop turn guide.

FIG. 4 is perspective view of an outer surface of an example opticalsensor loop turn guide.

FIG. 5 is a perspective view of an example optical sensor in a partiallyassembled state.

FIG. 6 is a perspective view of an example optical sensor in anassembled state.

FIG. 7 is a perspective view of an example mount wedge.

FIG. 8 is a perspective view of a collection of example tension rods.

FIG. 9 is a perspective view of another example optical sensor mountingsystem.

FIG. 10 is an exploded perspective view of another example opticalsensor mounting system.

FIGS. 11 and 12 are side and top views of the example optical sensormounting system of FIG. 10.

FIGS. 13-15 are various cross-sectional side views of the exampleoptical sensor mounting system of FIG. 10.

DETAILED DESCRIPTION

This document describes systems and techniques for mounting sensorattachments to drilling fluid piping on drilling rigs. The assembliesdescribed in this document can be used, for example, to mount opticalsensors such as sections of Sagnac loop interferometers to measureexpansion and contraction of the piping due to pressure variations inthe fluid flowing within the piping. The Sagnac Loop interferometer is asensor that can be used to detect mechanical or thermal disturbances orvibrations. The Sagnac interferometer operates by generating a lightsignal with a predetermined wavelength, transmitting the light signalthrough an optical fiber loop, and detecting the resulting coherentlight phase shift. Measurements of the shifts in the coherent lightphase provide information regarding physical disturbances or vibrationsalong the loop of the Sagnac interferometer.

In general, optical sensor mounts clamp, attach, or are otherwiseaffixed to an outside surface of one or more pipes in the drilling fluidpiping system. Fluid (for example, drilling fluid) flowing through thepipe exerts a pressure force outward against the pipe, which causessmall changes in the diameter of the pipe that vary with the pressure ofthe fluid within. The optical sensor mounts mechanically transfer, andin some implementations, amplify or reduce, changes in pipe diameter toone or more sensors. The signal outputs of such sensors can then beprocessed to observe changes in the diameter of the pipe. The changes indiameter of the pipe diameter may be processed using known physicalcharacteristics of pressure pipes, and detection of said changes canallow for downhole pressure pulse detection whereas said pressure pulsescan convey the specific information or data content.

FIG. 1 is a perspective view of an example optical sensor mountingsystem 100. In general, the mounting system 100 simplifies attachmentand removal of an optical sensor 101, such as a fiber optic loop sectionof a Sagnac Loop interferometer, a Mach-Zehnder interferometer, adistributed Acoustic Sensing System (DASS), or any other appropriatesensor that includes one or more loops of fiber optic cable, to and froma pipe 102 while preserving signal fidelity and rotational signalrejection of the optical sensor 101.

The optical sensor mounting system 100 includes a pair of mount wedges110 a and 110 b. The optical sensor 101 is wrapped around the peripheryof the pipe 102, and is removably affixed to the mount wedges 110 a, 110b by a pair of sensor loop turn guide assemblies 120 a and 120 b. Themount wedges 110 a, 110 b are flexibly interconnected by a collection oftension rods 130. The optical sensor 101 is wrapped around the pipe 102and is adjusted to a predetermined pre-tension by adjustment of thelinkage between the tension rods 130. The optical sensor 101 isconfigured to detect changes in the length of the optical sensor 101(e.g., stretching). In the illustrated configuration, expansion orcontraction of the circumference and diameter of the pipe 102 due tochanges in the pressure of a fluid within the pipe 102 will applychanges in tension on the optical sensor 101 that can be measured andused to determine changes in the fluid pressure within the pipe 102. Theoptical sensor 101, the mount wedges 110 a and 110 b, the sensor loopturn guide assemblies 120 a-120 b, and the tensioning rods 130 withassociated linkage will be discussed further in the descriptions ofFIGS. 2-9.

FIG. 2 is a perspective view of an example optical sensor loop 200. Theoptical sensor loop 200 includes a fiber optic cable 210 arranged in anelongated spiral having a middle section 220 in which the fiber opticcable 210 is arranged as a collection of generally planar andsubstantially parallel strands, and two end sections 230 in which thefiber optic cable 210 is arranged as a collection of generally planarand curved pathways. In some implementations the curved pathways may bearranged substantially concentric and semi-circular and/or in a partialelliptical arrangement.

The fiber optic cable 210 is terminated at each end by a pair of opticalcouplers 240. The optical couplers 240 provide connecting points towhich light sources, optical detectors, and other appropriate equipmentcan be optically coupled to the fiber optic cable 210.

FIGS. 3 and 4 are perspective views of an example optical sensor loopturn guide 300. FIG. 3 shows an optical sensor loop lower turn guide 301and FIG. 4 show an optical sensor loop upper turn guide 302. In general,the optical sensor loop lower turn guide 301 and the optical sensor loopupper turn guide 302 are coupled together to form the example sensorturn guide assembly 120 a of FIG. 1, and the optical sensor loop lowerturn guide 301 and the optical sensor loop upper turn guide 302 arecoupled together to form the example sensor turn guide assembly 120 b.

Referring to FIG. 3, an inner face 310 of the optical sensor loop lowerturn guide 301 is shown. The optical sensor loop lower turn guide 301includes a bore 330 and a collection of bores 350. The inner face 310includes a collection of grooves 320. The grooves 320 are arranged as acollection of ridges and troughs formed on the inner face 310 in acurved pathway. The grooves 320 are non-intersecting, and increaseoutwardly with increasing radii. In some implementations the curvedpathways may be arranged substantially concentric and semi-circularand/or in a partial elliptical arrangement. Each of the grooves 320 isconfigured to receive a portion of the optical fiber 210 at one of theend sections 230.

Referring to FIG. 4, the optical sensor loop upper turn guide 302 of thesensor loop turn guide 300 is shown. The optical sensor loop upper turnguide 302 includes the bore 330 and the bores 350. In someimplementations, the optical sensor loop upper turn guide 302 is asubstantially flat plate that, when assembled to the optical sensor looplower turn guide 301, contacts the ridges or the grooves 320 tosubstantially enclose and constrain the fiber optic cable 210 with eachof the grooves 320.

FIG. 5 is a perspective view of the example optical sensor 101 in apartially assembled state. As is best seen in reference to the sensorloop turn guide assembly 120 a, each loop of the end sections 230 of thesensor loop 200 is placed in one of the corresponding grooves 320 of theoptical sensor loop lower turn guide 301. The optical sensor loop upperturn guide 302 is placed adjacent the optical sensor loop lower turnguide 301, as is best seen in reference to the sensor loop turn guideassembly 120 b. In the assembled configurations of the sensor loop turnguide assemblies 120 a, 120 b, each mating pair of the optical sensorloop lower turn guide 301 and the optical sensor loop upper turn guide302 substantially surrounds and constrains a corresponding loop of thesensor loop 200.

A bottom sheath 510 is provided to support and protect the middlesection 220 of the sensor loop 200. Referring now to FIG. 6, which is aperspective view of the example optical sensor 101 in an assembledstate, a top sheath 610 is provided to support and protect the middlesection 220 of the sensor loop 200. The top sheath 610 includes holes620. The fiber optic cable 210 passes through the holes 620 to exposethe optical couplers 240.

The top sheath 610 and the bottom sheath 510 are flexible to allow thesensor loop to be bent into a curve. In some embodiments, the top sheath610 and the bottom sheath 510 can have a flexible stiffness that limitsthe bending radius of the sensor loop 200. For example, fiber opticcable 210 may have a maximum bending radius which, if exceeded, coulddamage the fiber optic cable 210 in a way that prevents light frompassing through and thus possibly causing the sensor loop 200 tomalfunction. The top sheath 610 and bottom sheath 510, however, can havea stiffness and bending radius that are greater than that of the fiberoptic cable 210, so that the sensor loop 200 will follow the relativelylesser bending radius of the sheaths 510, 610 when flexed.

Referring now to FIGS. 3-6, the sensor loop turn guides 300 also includethe collection of bores 350. During assembly, pairs of the sensor loopturn guides 301 and 302 are mated to align the bores 350, and acollection of fasteners (not shown) (e.g., bolts, screws) are passedthrough the bores 350 to removably attach the pairs to each other toform the sensor loop turn guide assemblies 120 a and 120 b. Duringassembly, the collection of fasteners are also passed through the bores350 to removably assemble the sensor loop turn guide assemblies 120 aand 120 b to the mount wedges 110 a and 110 b.

FIG. 7 is a perspective view of an example mount wedge 700. In someembodiments, the mount wedge 700 can be the mount wedge 110 a or themount wedge 110 b of FIG. 1. The mount wedge 700 includes a bottom face710, a back face 720, and a mount face 730.

The bottom face 710 is formed with a longitudinal concave curvature. Insome embodiments, the radius of the bottom face 710 approximates theradius of the pipe 102 of FIG. 1. The back face 720 is a substantiallyflat planar surface that intersects the bottom face 710 at anapproximately perpendicular angle. The front face 730 is a substantiallyflat planar surface that intersects the back face 720 at anapproximately 45 degree angle and intersects the bottom face 710 at anangle approximately tangent to the curvature of the bottom face 710. Insome embodiments, the angle at which the front face 730 and the backface 720 intersect can be determined from the diameter of pipe 102,

The front face 730 includes a groove 740. The groove 740 is asemi-cylindrical, concave recess formed along the longitudinal length(e.g., relative to the axis of curvature of the bottom face 710) of adistal end 702 of the mount wedge 700. A slot 750 cut out of the distalend 702, intersecting the groove 740 near a midpoint substantiallyperpendicular to the groove 740. A longitudinal bore 760 is formedthrough the mounting wedge substantially parallel to the faces 710, 720,and 730. The groove 740, the slot 750, and the bore 760 will bediscussed further in the descriptions on FIGS. 8 and 9.

The front face 730 also includes a mounting post 770. The mounting post770 protrudes out from the mount wedge 700 at an angle substantiallyperpendicular to the front face 730. The mounting post 770 is configuredto mate with the bores 330 of the sensor loop turn guides 300, as willbe discussed further in the descriptions on FIG. 9. In some embodiments,the mounting post 770 may be a threaded member that can be removablythreaded into a corresponding threaded receptacle in the front face 730.

FIG. 8 is a perspective view of the collection of example connector rods130. The collection includes an outer rod 810 a, an outer rod 810 b, acenter rod 820, a through-wedge rod 830 a, and a through-wedge rod 830b. The outer rods 810 a and 810 b have a diameter that approximates oris less than that of the groove 740 of the example mount wedge 700 ofFIG. 7. The outer rods 810 a, 810 b and the center rod 820 each includea bore 840. The bores 840 are formed near the midpoints andperpendicular to the longitudinal lengths of their corresponding rods810 a, 810 b, and 820.

The through-wedge rods 830 a and 830 b have a diameter that allows therods 830 a, 830 b to be inserted into the bore 760. The through-wedgerods 830 a and 830 b each also include a pair of bores 850, with eachbore 850 formed near an end and perpendicular to the longitudinallengths of their corresponding through-wedge rods 830 a and 830 b. Thecollection of rods 130 will be discussed further in the description ofFIG. 9.

FIG. 9 is another perspective view of the example optical sensormounting system 100 in a partly assembled form. During assembly, themount wedges 110 a and 110 b are arranged such that their bottom faces710 are in contact with the pipe 102, and their back faces 720 arefacing each other. The sensor loop turn guide assembly 120 a is broughtinto contact with the mount wedge 110 a such that the mount post 770passes through the bores 330 such that one of the bottom faces 710contacts the front face 730. A fastener (not shown) (e.g., bolt, screw,rivet) is passed through each of the bores 350 to removably attach thesensor loop turn guide assembly 120 a to the mount wedge 110 a.

The optical sensor 101 is wrapped around the pipe 102, and the sensorloop turn guide assembly 120 b is assembled to the mount wedge 110 b ina manner similar to the assembly of the turn guide assembly 120 a andthe mount wedge 110 a (e.g., as illustrated in FIG. 1). Thethrough-wedge rod 830 a is inserted into the bore 760 in the mount wedge110 a, and the through-wedge rod 830 b is inserted into the bore 760 inthe mount wedge 110 b.

The outer rod 810 a is placed in the groove 740 of the mount wedge 110a, and the outer rod 810 b is placed in the groove 740 of the mountwedge 110 b. The center rod 820 is placed between the mount wedges 110 aand 110 b. The bores 840 in outer rod 810 a, the outer rod 810 b, andthe center rod 820 are aligned with the slots 750 and with each other. Afastener (not shown) (e.g., a bolt, a screw) is passed through thealigned bores 840 and is adjustably tensioned. Tension on the fastenerdraws the mount wedges 110 a and 110 b toward each other, which in turnapplies an adjustable pre-tension on the optical sensor 101. In someembodiments, the bores 850 of the rods 830 a and 830 b can be aligned, acollection of fasteners (not shown) can be passed through the bores 850and adjustably tensioned to pre-tension the optical sensor 101 insteadof or in addition to use of the outer rods 810 a, 810 b.

FIG. 10 is an exploded perspective view of another example opticalsensor mounting system 1000. FIGS. 11 and 12 are side and top views ofthe optical sensor mounting system 1000. FIGS. 13-15 are variouscross-sectional side views of the optical sensor mounting system 1000.

With reference to FIGS. 10-15, the optical sensor mounting system 1000removably attaches an optical sensor loop (not shown), such as theexample optical sensor loop 200 of FIG. 2, to the pipe 102. The opticalsensor mounting system 1000 includes a support wedge 1010 having abottom face 1012, a side face 1014 a, a side face 1014 b, and a groove1016.

The bottom face 1012 is formed with a concave angular or curved profilethat approximates the outer diameter of the pipe 102. The side faces1014 a, 1014 b are substantially planar faces that intersect the bottomface 1012 at angles approximately tangent to the outer diameter of thepipe 102, and approach but do not intersect each other at the groove1016.

The optical sensor mounting system 1000 includes a tension bar 1020. Acollection of load transfer pins 1022 extend laterally outward from thetension bar 1020. The tension bar 1020 is positioned in the groove 1016such that the load transfer pins 1022 align with and extend through acorresponding collection of lateral slots 1018 formed in the side faces1014 a and 1014 b, intersecting the groove 1016. A collection of bores1024 are formed through the tension bar 1020 perpendicular to the loadtransfer pins 1022.

A collection of fasteners 1030 (e.g., bolts) are passed through andprotrude out the bottoms of the bores 1024. A collection of springs 1032are placed about the protruding ends of the fasteners 1030, and thefasteners 1030 are threaded into a collection of bores 1019 formed inthe groove 1016, capturing the springs 1032 between the support wedge1010 and the tension bar 1020. The fasteners 1030 are tensioned toadjustably draw the tension bar 1020 toward the support wedge 1010against the bias of the springs 1032. As the tension bar 1020 is drawninto the groove 1016, the load transfer pins 1022 are drawn along thelateral slots 1018 toward the pipe 102.

The optical sensor mounting system 1000 includes a sensor loop turnguide 1040 a and a sensor loop turn guide 1040 b. The sensor loop turnguides 1040 a, 1040 b each have a front face 1042 and a back face 1044.The back faces 1044 are substantially flat surfaces. Each of the frontfaces 1042 includes a collection of grooves 1046. The grooves 1046 arearranged as a collection of concentric, semi-circular ridges and troughsformed on the front faces 1042. The grooves 1046 are non-intersecting,and increase outwardly with increasing radii. Each of the grooves 1046is configured to receive a portion of the optical fiber 210 of FIG. 2 atone of the end sections 230.

The sensor loop turn guide 1040 a is removably assembled to the supportwedge 1010 by placing the back face 1044 in contact with the side face1014 a. The load transfer pins 1022 extend through a collection of bores1048 formed through the sensor loop turn guide 1040 a. Similarly, thesensor loop turn guide 1040 b is removably assembled to the supportwedge 1010 by placing the back face 1044 in contact with the side face1014 b. The load transfer pins 1022 extend through a collection of bores1048 formed through the sensor loop turn guide 1040 b.

In an assembled form, the sensor loop turn guides 1040 a and 1040 b drawthe optical sensor loop 200 about a section of the outer periphery ofthe pipe 102. As the fasteners 1030 are partly unthreaded, the springs1032 urge the tension bar 1020 away from the pipe 102, adjustablytensioning the optical sensor 200 about the pipe 102.

In operation, pressurization of a fluid within the pipe 102 can causethe pipe 102 to expand. Expansion of the pipe 102 can provide additionaltension to the optical sensor loop 200 as it is held to the pipe 102 bythe mounting system 100 of FIGS. 1-9 or the mounting system 1000 ofFIGS. 10-15. In some implementations, light passing through the opticalsensor loop 200 can be affected by varying the tension applied to theoptical sensor loop 200, and these effects can be measured. For example,by measuring the effects of tension on the light being passed throughthe optical sensor loop 200, expansion and contraction of the pipe 102caused by pulses of fluid pressure within the pipe 102 can be measured.

Although a few implementations have been described in detail above,other modifications are possible. For example, the assembly flowsdiscussed in the descriptions of the figures do not require theparticular order described, or sequential order, to achieve desirableresults. In addition, other steps may be provided, or steps may beeliminated, from the described flows, and other components may be addedto, or removed from, the described systems. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A system for removably attaching an optical fibersensor loop onto a tubular member, said system comprising: an opticalfiber sensor loop having a continuous optical fiber arranged in aplurality of loops, each of said loops having a first end turn and asecond end turn; a first turn guide including a plurality of turngrooves, each of said turn grooves configured to receive a portion ofthe optical fiber at the first end turn; a second turn guide including aplurality of turn grooves, each of said turn grooves configured toreceive a portion of the optical fiber at the second end turn; a firstsupporting wedge having a first surface configured to receive the firstturn guide and a second surface configured to be received on a firstportion of an outer surface of the tubular member; a second supportingwedge having a first surface configured to receive the second turn guideand a second surface configured to be received on second portion of anouter surface of the tubular member; and a connector configured tocouple the first supporting wedge to the second supporting wedge.
 2. Thesystem of claim 1, wherein the turn grooves are arranged substantiallyconcentric and semi-circular.
 3. The system of claim 1 furthercomprising: a first compression plate configured to be removably securedon the first turn guide over the first end turn of the optical fiberdisposed in each turn groove of the first turn guide; and a secondcompression plate configured to be removably secured on the second turnguide over the second end turn of the optical fiber disposed in eachturn groove of the second turn guide.
 4. The system of claim 1 furthercomprising: a mounting post on the first surface of the first supportingwedge and a second mounting post on the first surface of the secondsupporting wedge; and a first mounting opening in the first turn guideconfigured to receive the first mounting post and a second mountingopening configured to receive the second mounting post.
 5. The system ofclaim 1, wherein the connector comprises: a groove disposed in the firstsurface of the first supporting wedge and a groove in the first surfaceof the second supporting wedge; a first rod configured to be received inthe groove of the first supporting wedge and a second rod configured tobe received in the groove of the second supporting wedge; and a couplingmember for coupling the first rod to the second rod.
 6. The system ofclaim 5, wherein the coupling member includes a tension adjustingdevice.
 7. The system of claim 6, wherein the tension adjusting devicecomprises a bolt positionable through an opening through the first rodand an opening through the second rod with at least one end of the boltthreaded to receive a mating threaded nut.
 8. The system of any of claim1, wherein the optical fiber sensor loop is selected from a groupcomprising one or more of: a section of a Sagnac interferometer, asection of a Mach-Zehnder interferometer, and a section of a distributedAcoustic Sensing System (DASS).
 9. The system of claim 8, wherein theturn grooves are arranged substantially concentric and semi-circular.